A plastic web can be made with an extrusion apparatus comprising a plastic-material displacing screw press, a metering pump with a volume flow rate depending on rotation speed, a wide-mouth or broad-slit output die and a rolling unit with a plurality of smoothing rolls in which the flow of a melt of thermoplastic material is regulated by the metering pump and a melt web issuing from the output die is cooled and calibrated in the rolling unit.
The rotation speed of the metering pump and the peripheral speed of the smoothing rolls are adjusted or set depending on each other to preserve a steady flow.
By "plastic web" I mean a plastic foil, a plastic laminate web or plastic plate.
In the known process, an adjustment of the peripheral speed of the smoothing rolls depending on the rotation speed of the metering pump is performed manually.
Generally the peripheral speed and the rotation speed can be kept constant by regulating steps or features. The manual adjustment occurs by an operator according to visual observations of the plastic web being extruded. Furthermore the melt bulge or bank upstream of the gap or nip between the calendaring rolls is observed. The quality of the plastic web in regard to thickness, the shape of the thickness profile and the surface depends on the experience of the operator. Unavoidable variations of the rotation speed and thus the volume flow rate of the metering pump cannot be taken into account during operation and can impair of the quality of the product.